The present invention relates to systems and methods for controlling an internal combustion engine during and shortly after starting.
Optimal control of internal combustion engines during starting presents a number of challenges. Conventional strategies provide a rich (excess fuel) air/fuel ratio charge during cranking and run-up with advanced ignition timing to achieve stable combustion. Spark feedback control of engine speed is then used during idling to compensate for disturbances such as operation of vehicle accessories.
To reduce feedgas emissions during cranking and startup, and to reduce the time required for any catalyst to become operational, ignition timing may be retarded along with air/fuel enleanment during the first twenty or more seconds after starting. These cold start operating conditions present significant difficulty in that they can approach and exceed engine operational stability boundaries and are increasingly susceptible to disturbances and wear/aging factors. Current control strategies require compromises during these operating conditions from optimal ignition timing and air/fuel calibration to avoid rough operation, speed oscillations, and/or stalling. Engine calibration compromises must also accommodate manufacturing variation, changing environmental conditions (especially humidity), and component aging and wear.
An object of the present invention is to provide a system and method for controlling an internal combustion engine during and shortly after starting to provide improved engine stability and reduced emissions by controlling combustion burn location via ignition timing.
In carrying out the above object and other objects, advantages, and features of the present invention, a system and method for controlling an internal combustion engine include providing a cylinder charge with an air/fuel ratio slightly lean of stoichiometry and controlling combustion burn location retarded from that of MBT using ignition timing to compensate for engine operational difficulties during starting.
The present invention provides a number of advantages. For example, the present invention minimizes calibration tradeoffs previously required to maintain stable combustion during and shortly after starting to reduce feedgas emissions, increase exhaust gas heat flow, and reduce catalyst light-off time. Engine cold start control based on combustion burn location allows for more aggressive spark retard and allows the air/fuel ratio to be maintained slightly lean of stoichiometry while maintaining engine stability and reducing roughness, speed oscillations, and stalls.